The invention relates to a phosphoric acid fuel cell and more particularly to integral edge seals for a phosphoric acid fuel cell.
Phosphoric acid fuel cells provide an environment for an electrochemical reaction between a fuel and oxidant to create electrical energy. The fuel cells may be any shape. However, they are normally rectangular and stacked one on top of another. A stack of fuel cells, so formed, have manifolds disposed on opposite sides of the stack for supplying fuel and oxygen to the cells and for removing spent gases from the cells. The cells are disposed between bipolar plates made of graphite with a plurality of grooves on opposite sides thereof to either supply fuel, such as hydrogen, to the anode and oxidant, such as oxygen in the form of air, to the cathode. The anode assembly is formed by providing a layer of catalyst on a graphite backing. The cathode is also formed by providing a catalytic layer on graphite backing paper. Between the catalytic layers of the anode and the catalytic layer of the cathode is a porous matrix and an insulator such as a silicon carbide layer. The silicon carbide is disposed adjacent the cathode or anode and acts as an electron insulator to prevent electrons from traveling within the cell from the anode assembly to the cathode assembly. The catalytic layer of the anode assembly, the catalytic layer of the cathode assembly, the silicon carbide layer and the matrix are sufficiently porous to allow the electrolyte, phosphoric acid, to permeate therethrough. The catalyst in combination with the high temperature of the anode gases causes the hydrogen to ionize. The hydrogen ions conduct through the electrolyte to react with the oxygen in the catalytic layer of the cathode. The electrons freed when creating the hydrogen ions flow through the conductive bipolar plate to the cathode in the adjacent cell to form an electrical potential.
U.S. Pat. No. 3,867,206 describes wet seals for fuel cells wherein the edges of the electrodes are impregnated with particular material to reduce the pore size adjacent the edges so that when permeated with electrolyte a seal is formed due to the capillary action of the reduced pore size.
U.S. Pat. No. 3,846,176 describes encasing the fuel cell in molded plastic.